多壁碳纳米管的纯化及其表面含氧基团的表征

用兼具酸性和氧化性的HNO3水溶液可方便地除去残留在原生态多壁碳纳米管(CNT)上的Ni-MgO催化剂组分,同时在其表面产生某些含氧官能团,使原生态多壁碳纳米管的疏水性表面变为亲水性表面.采用Boehm中和滴定法以及X射线衍射(XRD)、热脱附谱(TPD)、傅里叶变换红外(FTIR)光谱和X射线光电子能谱(XPS)等技术对HNO3处理过的多壁碳纳米管的相组成和表面含氧官能团进行测量和表征.结果表明:所生成表面含氧官能团的总量以经7.0mol·L-1硝酸378K处理24h的CNT为最高;3种主要表面含氧官能团的含量高低顺序为,羧基内酯型羧基酚型羟基.     

碳纳米管在接枝二元胺过程中微结构的变化

通过对酸化的多壁碳纳米管(MWNTs)进行酰氯化, 在碳纳米管表面接枝己二胺. 用红外光谱、热重分析、拉曼光谱和场发射扫描电镜对处理前后的碳纳米管进行分析表征. 结果表明, 经过酰氯活化, 己二胺比较容易被接枝到碳纳米管上. 而且还发现碳纳米管在酸化后形成紧密块状结构, 在接枝胺后重新变得蓬松, 其表观比容甚至大于原始碳纳米管. 从理论上分析了碳纳米管的反应过程, 对碳纳米管在接枝胺过程中微结构的变化机理进行推测, 认为通过接枝, 己二胺插入碳纳米管之间, 改变了碳纳米管之间的相互作用, 使得酸化后因形成氢键而导致的紧密堆砌结构被破坏.     

单壁碳纳米管短管的制备

分别通过控制CVD生长时间的方法和在混合的硝酸硫酸中超声氧化碳纳米管的化学剪裁法制备了单壁碳纳米管短管.两种方法都能将大多数碳纳米管的长度控制在500 nm以下.拉曼光谱结果表明: 在化学剪裁过程中,单壁碳纳米管部分被破坏产生无定形碳杂质;用控制CVD反应时间得到的单壁碳纳米管短管样品比长时间反应得到的长管样品杂质少,且不存在后处理时碳纳米管的破损问题,其纯度比化学剪裁法得到的产品纯度高.     

聚乙酰苯胺修饰碳纳米管载铂催化剂对甲醇电催化氧化

以原位化学聚合的聚乙酰苯胺/多壁碳纳米管(PAANI-MWCNTs)复合纳米材料作为载体,采用硼氢化钠还原法将Pt纳米粒子担载到PAANI-MWCNTs复合纳米材料表面,制备了Pt/PAANI-MWCNTs复合纳米催化剂.样品的结构和形貌用紫外-可见(UV-Vis)光谱、拉曼光谱、扫描电镜(SEM)、透射电镜(TEM)和X射线衍射(XRD)进行了表征.结果表明,聚乙酰苯胺与碳纳米管之间存在较强的π-π相互作用,使其能牢固地吸附于多壁碳纳米管表面,对碳纳米管的结构完整性和导电性有一定的改善作用.同时,金属Pt纳米颗粒较为均匀地分散在PAANI-MWCNTs表面,粒径分布范围较窄.采用循环伏安法和计时电流法在酸性溶液中研究了Pt/PAANI-MWCNTs催化剂对甲醇的电催化氧化活性,结果表明Pt/PAANI-MWCNTs复合纳米催化剂比用混酸处理的碳纳米管载铂催化剂对甲醇呈现出更高的电催化氧化活性和更好的抗中毒能力及稳定性.     

分光光度法测定三氧化铀中的硫酸根

采用TBP-萃淋树脂吸附三氧化铀样品中的铀,硫酸根与铬酸钡进行交换反应后,直接比色法测定硫酸根的含量。实验中研究了三氧化铀样品中硫酸根含量测定的样品制备、分离、反应酸度,煮沸时间,铬酸钡用量等影响因素。优化条件下,采用硝酸(5mol/L)淋洗、1mL HCl溶液(2.5mol/L)调节溶液中酸浓度、使用2mL BaCrO_4进行交换反应、煮沸3min,得到方法相对标准偏差小于10%,加标回收率为92.9%～110%。实验结果表明,直接显色的测定方法灵敏、快速、准确度高。方法测定条件易于获得,适于推广应用。     

纳米三氧化钨修饰碳纳米管载铂催化剂对甲醇氧化的电催化性能

采用表面修饰技术将碳纳米管(CNT)表面羧基化, 通过羧基将钨离子基团修饰到碳纳米管的外表面, 再通过高温焙烧处理将钨离子基团氧化成WO₃, 成功合成了纳米WO₃/CNT复合物, 进一步还原Pt 的前驱体而得到Pt-WO₃/CNT复合催化剂. 采用X射线粉末衍射(XRD)和透射电镜(TEM)对样品的形貌和晶型结构进行了表征, 结果表明, Pt纳米粒子为面心立方晶体结构, 均匀地分布在WO₃修饰的碳纳米管表面. 采用循环伏安(CV)和计时电流法研究了在酸性溶液中Pt-WO₃/CNT催化剂对甲醇的电催化氧化活性, 结果表明WO₃修饰的碳纳米管载铂催化剂比用混酸处理的碳纳米管载铂催化剂对甲醇呈现出更高的电催化氧化活性和更好的稳定性.     

液相法制备取向ZnO纳米线阵列的场发射特性(英文)

采用水热合成工艺,在不同条件下制备了不同的一维取向ZnO纳米线阵列样品.用X射线衍射仪(XRD)、扫描电镜(SEM)及透射电镜(TEM)对样品的晶体结构和形貌等进行了表征,对样品的场发射特性进行了分析和比较,并用Fowler-Nordheim方程对影响ZnO纳米线场发射的因素进行了研究.结果表明,具有较低生长密度分布、较高的长径比和较尖锐生长端的ZnO纳米线阵列样品具有较好的场发射特性.     

两步法制备多孔硅及其表征I:恒电流法(英文)

本工作通过采用电化学极 -化学氧化两步法在 1:1氢氟酸和乙醇溶液中制备出孔径约为 1～ 2 μm ,厚度大经为 6～ 10 μm的多孔硅样品 .首先将 0 .0 3A/cm2 的恒电流施加到p( 10 0 )硅片一段时间 ,然后将该硅片浸到 2 0 %的硝酸溶液中氧化一段时间 .通过此方法获得的多孔硅结构再进一步用扫描电子显微镜和拉曼光谱仪进行表面形貌和光学性质的考察 .所有制备出的多孔硅结构均有光致发光现象 .老化的多孔硅样品 (在干燥器放置一年 )的光致发光谱峰强度明显增强 ,但分别经过苯乙烯和十六碳烯 ( 1)两种有机溶剂处理 1h后的老化多孔硅样品的光致发光强度却没有显著改变 .     

压缩集结碳纳米管电极对活性艳红染料的电催化降解研究

采用浓硝酸回流、高温焙烧、高温焙烧结合高速球磨的方法对碳纳米管进行前处理. 通过低温氮吸附法测定碳纳米管的比表面积; 透射电子显微镜观察碳纳米管处理前后的形貌结构; 红外光谱分析碳纳米管处理前后的官能团变化; 拉曼光谱分析处理前后的碳纳米管中无定形碳和石墨碳含量的变化; 将处理前后的碳纳米管制成电极, 作为电催化阳极来处理模拟染料废水活性艳红X-3B溶液. 实验结果表明: 经处理后制成的碳纳米管电极, 其稳定性及对染料溶液的电催化降解效率都有显著提高, 高温焙烧结合高速球磨为最佳的前处理方法.     

碳纳米管阵列的气相沉积制备及场发射特性

运用酞菁铁热解法气相沉积制备了碳纳米管阵列.所得碳纳米管呈多壁结构.单根碳纳米管的平均直径约为25 nm，长度约4～5 μm，且具有很好的准直性.研究了碳纳米管阵列的平面场发射特性，相应的开启电压和阈值电压分别为1.28和2.3 V•μm－1，表明碳纳米管具有很强的场发射能力.利用场发射显微镜观察了碳纳米管阵列的场发射像，发现碳纳米管阵列的场发射主要集中在样品薄膜的边缘部位.这是由于碳纳米管密度过大而产生的屏蔽效应所致.     

Enhancement of Field Emission Characteristics for Multi-Walled Carbon Nanotubes Treated with a Mixed Solution of Chromic Trioxide and Nitric Acid

A simple acid treatment method was applied to functionalize the surface and to modify the structures of multi-walled carbon nanotubes (CNTs) grown on silicon substrates using a mixed solution of chromic trioxide (CrO₃) and nitric acid (HNO₃). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and energy dispersive spectrometer (EDS) were employed to investigate the mechanism causing the modified field emission (FE) properties of the CNT films. After 20 min of CrO₃+HNO₃ treatment, the emitted currents were enhanced by more than one order of magnitude compared with those of the untreated CNTs. This large increase in emitted current can be attributed to the favorable surface morphologies, open-ended structures, and highly curved CNT surfaces in the CNT films. These factors altogether caused an increase in the field enhancement factors of CNTs. We also demonstrated that using a mixed solution of CrO₃+HNO₃ post-treatment exhibited a higher emission current and a lower turn-on electric field than in the CNTs treated with HNO₃. The method provides a simple, economical, and effective way to enhance the CNT field emission properties.     

Prussian Blue/Multiwalled Carbon Nanotube Hybrids: Synthesis,Assembly and Electrochemical Behavior

Prussian blue/carbon nanotube (PB/CNT) hybrids with excellent dispersibility in aqueous solutions were synthesized by adding CNTs to an acidic solution of Fe³⁺, [Fe(CN)₆]^3? and KCl. Fourier transform infrared spectroscopy, UV‐vis absorption spectroscopy and scanning electron microscopy were employed to confirm the formation of PB/CNT hybrids. The PB nanoparticles formed on the CNT surfaces exhibit a narrow size distribution and an average size of 40 nm. The present results demonstrate that the selective reduction of Fe³⁺ to Fe²⁺ by CNTs is the key step for PB/CNT hybrid formation. The subsequent fabrication of the PB/CNT hybrid films was achieved by layer‐by‐layer technique. The thus‐prepared PB/CNT hybrid films exhibit electrocatalytic activity towards H₂O₂ reduction.     

Quantitative analysis of electron field-emission characteristics of individual carbon nanotubes: the importance of the tip structure

Electron field-emission measurements on individual carbon nanotubes (CNTs) were performed inside the transmission electron microscope (TEM). The field-emission characteristics of CNTs with different tip structures were compared, and their field conversion factor and emission area were studied systematically. It was found that the field-emission characteristics of a CNT depend sensitively on its tip structure, and in particular an opened CNT was shown to be superior to a capped CNT. High-resolution TEM observations revealed that the tip of an opened CNT may, in general, be regarded as being composed of irregular shaped graphitic sheets, and these graphitic sheets have been found to improve dramatically the field-emission characteristics, but the sharp edge may result in larger error in the calculated emission area. The influence of uncertainty in the work function of the CNTs on the field conversion factor and emission area calculation was also investigated.     

Bulk synthesis of linear carbon chains confined inside single-wall carbon nanotubes by vacuum discharge

Carbyne, an infinite carbon chain, has attracted much interest and induced significant controversy for many decades. Recently, the presence of linear carbon chains (LCCs), which were confined stably inside double-wall carbon nanotubes (DWCNTs) and multiwall carbon nanotubes (MWCNTs), has been reported. In this study, we present a novel method to produce LCCs in a film of carbon nanotubes (CNTs). Our transmission electron microscopy and Raman spectroscopy revealed the formation of a bulk amount of LCCs after electric discharge of CNT films, which were used as field emission cathodes. The LCCs were confined inside single-wall CNTs as well as DWCNTs. Furthermore, two or three LCCs in parallel with each other are encapsulated when the inner diameter of CNT is larger than approximately 1.1 nm.     

Carbon nanotube bags: catalytic formation, physical properties, two-dimensional alignment and geometric structuring of densely filled carbon tubes

The catalytic CVD synthesis, using propyne as carbon precursor and Fe(NO3)3 as catalyst precursor inside porous alumina, gives carbon nanotube (CNT) bags in a well-arranged two-dimensional order. The tubes have the morphology of bags or fibers, since they are completely filled with smaller helicoidal CNTs. This morphology has so far not been reported for CNTs. Owing to the dense filling of the outer mother CNTs with small helicoidal CNTs, the resulting CNT fibers appear to be stiff and show no sign of inflation, as sometimes observed with hollow CNTs. The fiber morphology was observed by raster electron microscopy (REM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The carbon material is graphitic as deduced from spectroscopic studies (X-ray diffraction, Raman and electron energy-loss spectroscopy (EELS)). From M?ssbauer studies, the presence of two different oxidation states (Fe0 and FeIII) of the catalyst is proven. Geometric structuring of the template by two different methods has been studied. Inkjet catalyst printing shows that the tubes can be arranged in defined areas by a simple and easily applied technique. Laser-structuring creates grooves of nanotube fibers embedded in the alumina host. This allows the formation of defined architectures in the microm range. Results on hydrogen absorption and field emission properties of the CNT fibers are reported.     

A general route to prepare one- and three-dimensional carbon nanotube/metal nanoparticle composite nanostructures

Adsorption of polyethyleneimine (PEI)-metal ion complexes onto the surfaces of carbon nanotubes (CNTs) and subsequent reduction of the metal ion leads to the fabrication of one-dimensional CNT/metal nanoparticle (CNT/M NP) heterogeneous nanostructures. Alternating adsorption of PEI-metal ion complexes and CNTs on substrates results in the formation of multilayered CNT films. After exposing the films to NaBH4, three-dimensional CNT composite films embedded with metal nanoparticles (NPs) are obtained. UV-visible spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy are used to characterize the film assembly. The resulting (CNT/M NP)n films inherit the properties from both the metal NPs and CNTs that exhibit unique performance in surface-enhanced Raman scattering (SERS) and electrocatalytic activities to the reduction of O2; as a result, they are more attractive compared to (CNT/polyelectrolyte)n and (NP/polyelectrolyte)n films because of their multifunctionality.     

Clar valence bond representation of pi-bonding in carbon nanotubes

The application of the Clar aromatic sextet valence bond (VB) model to extended, defect-free single-walled carbon nanotubes (CNTs) with roll-up vectors (m, n) provides a real space model of their electronic structure. If m - n = 3k, where k is an integer, then all pi-electrons can be represented by aromatic sextets, and the CNT is fully benzenoid; the converse is also true. Since m - n = 3k is known to be a necessary criterion for conductivity in CNTs, only fully benzenoid CNTs are metallic, and only potentially metallic CNTs are fully benzenoid. This behavior contrasts with that of planar polycyclic aromatic hydrocarbons, in which the fully benzenoid structures are known to have large HOMO-LUMO gaps. For CNTs that are not fully benzenoid, e.g., m - n = 3k + l, where l = 1 or 2 and k is an integer, a seam of double bonds wraps about an otherwise benzenoid CNT at the chiral angle - 60 degrees or the chiral angle, respectively. Nucleus-independent chemical shift calculations on hydrogen-terminated CNT segments support this, and show that the magnetic manifestation of aromatic sextets is not due to electron correlation. The resonance hybrid of the Clar VB structures corresponds to patterns occasionally observed in scanning tunneling microscopy images of CNTs.     

Effects of pH on electrocatalytic activity of functionalized carbon nanotubes

In this study, we modified carbon nanotubes (CNTs) by grafting with poly(ethylene glycol) (PEG) using the “grafting to” method. The PEG-grafted CNT (CNT-g-PEG) was cast on indium tin oxide (ITO) electrode to investigate the electrocatalytic activity of CNT to the redox reactions of the Fe(CN)₆^3−/4−as a probe using cyclic voltammetry and electrochemical impedance spectroscopy. The electrocatalytic activity of CNT was correlated with CNT dispersion in the cast film on ITO as a function of pH of aqueous solution from which the film was cast. The CNT dispersions in aqueous solutions of different pH and in the cast films were examined by visual observation and zeta potential, scanning electron microscopy and transmission electron microscopy, respectively. At a pH in the range of 3–11 at which ITO electrode was modified, two functionalized CNT (fCNT and CNT-g-PEG) were both found to electrocatalyze the redox reactions of the Fe(CN)₆^3−/4−probe and the PEG grafts in CNT-g-PEG could help CNT adhere to the electrode to obtain durable modified electrode. The more uniform CNT dispersions in aqueous solutions and in the cast films appeared to have greater electrocatalytic acitivity.     

Enhancement mechanism of field electron emission properties in hybrid carbon nanotubes with tree- and wing-like features

In this work, the tree-like carbon nanotubes (CNTs) with branches of different diameters and the wing-like CNTs with graphitic-sheets of different densities were synthesized by using plasma enhanced chemical vapor deposition. The nanostructures of the as-prepared hybrid carbon materials were characterized by scanning electron microscopy and transmission electron microscopy. The structural dependence of field electron emission (FEE) property was also investigated. It is found that both of the tree- and wing-like CNTs exhibit a lower turn-on field and higher emission current density than the pristine CNTs, which can be ascribed to the effects of branch size, crystal orientation, and graphitic-sheet density.     

溶液法制备的碳纳米管薄膜的结构分析与场致电子发射机理研究

结合紫外光电子能谱和拉曼光谱对溶液法制备的碳纳米管薄膜的场致电子发射性能进行研究。采用溶液滴涂法制备的碳纳米管薄膜的场致电子发射开启电场约为3.33 MV/m,阈值电场约为5.44 MV/m,以福勒-诺得海姆(Fowler-Nordheim,FN)理论对电子发射进行解释,其发射的增强因子接近103。通过对紫外光电子能谱的分析,发现碳纳米管薄膜的低能量截止端在外加电场作用下逐步降低,表明纳米管薄膜的表面有效势垒在外加电场作用下逐步下降,从而使得碳纳米管薄膜的电子更加容易发射进入真空。结合拉曼光谱和电学特性的研究,发现界面过渡层的接触电阻与碳纳米管薄膜中的非晶碳成分均可以增强场致电子发射。